What Is Conversion Rate Optimisation (CRO)

What is Conversion Rate Optimization (CRO)

What Is A Conversion?

Before we can answer what is conversion rate optimisation? We need to understand what a conversion is. Every website or app has a purpose, an action(s) or a task(s) that the website owner expects a user to complete. Depending on the nature of the website, this could be:

[list 1]

  • making a purchase (eCommerce)
  • reading multiple articles (publishing)
  • placing a bet (gaming)
  • requesting a quote/filling in a form (insurance),
  • subscribing to a newsletter
  • making a phone call
  • uploading a photo (social media sites)
  • sharing some content (social media sites)
  • downloading an app
  • creating an account
  • making a deposit (banking)
  • booking a table/holiday (restaurant/travel)
  • downloading a file
  • swiping left and right (dating)
  • perform a search (Google)
  • …etc

These are just a handful of tasks that I can think of. In reality there are probably countless more and new ones are being added all the time. A user might be able to complete multiple actions on a website, but there is usually a primary action which is the Golden Action that website owners want the user to make, the simplest case being making a purchase and exchanging money for some goods or service. There might be a set of sub-actions a user might to take before making a purchase, but making that purchase is likely to be the most important.

If a website allows a user to do any of the above, that is called a conversion.

What is a Conversion Rate?

Quite simply, a conversion rate is the percentage of users completing an action.

Conversion Rate (%) = Unique Conversions / Users

Each action is measured in isolation of other actions. That is to say, you wouldn’t sum up making a purchase and downloading an app and then try to calculate the percentage of users completing those actions. Why not? For one, it’s just ridiculous, but logically a user can do both actions in this case, making the rate of conversion meaningless. Similarly you might choose to measure unique conversions to ensure you’re not inflating your conversion rate by counting actions from one user multiple times.

The “conversion” in the above formula can be anything from that list, it can be a call rate, booking rate, swipe rate, subscription rate, download rate, etc… When it comes to measuring your conversion rate, you can have anything you want, just ensure it makes sense for your business. Ultimately the key is to understand your business well enough to know what the most important metric for you is.

User Goals

Put it another way, although we call it a conversion, to the user it’s called a goal. They’ve come to your website to achieve something, to reach their goal. This could be anything from [list 1]. In many cases they may not even realise that their goal is something from that above list. No one goes to a newspaper website with the aim to download an app, they go there to consume content. If they’re doing it frequently enough, it’s your job to recognise their goal and then offer them the app or show them other relevant articles to get them to read more and stay on the site. By helping users achieve their goal, you can improve your conversion rate.

Conversion Rate Optimisation (CRO)

Therefore, conversion rate optimisation (CRO) is the process of improving or optimising the percentage of users who complete the desired action or task. e.g. increase the percentage of users who make a purchase, download an ebook, upload a photo, place a deposit etc…

The way you improve your conversion rate will vary depending on the task you want the user to complete or the purpose of your website. I won’t list out how you can go about improving your conversion rate as that is beyond the purpose of this post but a good place to start is to look at how you can improve your Micro Conversions.

Micro Conversions

In the first section I mentioned a user may need to complete a series of sub-actions in order to reach their goal (or convert). For example, filling in each section of the form before they submit it or building a product before they buy it. These are called micro-conversions, the small steps that a user needs to take to reach their macro goal. The more complicated these micro-conversions are, the less likely the user is going to be to achieve what they came for.

User Experience

Which brings me onto user experience. Whether a user converts or not ultimately comes down to the experience they have. If the site is slow, doesn’t work, prices are wrong, delivery is expensive, the forms are too long, the content is rubbish, etc… they aren’t going to do whatever it is they came to do. The job of a Conversion Rate Optimiser is to improve this experience. Sometimes the question a CRO’er may have to ask is not “what’s wrong with the site?” but rather “how can it better?”. Keep in mind that most sites will do what they were made to do and for users who have no choice but to complete the task they’ll find a way, even if the experience is shit. It’s the users who do have a choice, they’re the ones who will leave at the first hurdle they face.


What separates the field of CRO and literally any other field where someone is trying to improve the user experience is the ability to quantify the changes made.

One might argue that just making the change and measuring the pre and post conversion rate should be enough. Well it’s not. Let me be very clear about that. By all means use it as a guide but the circumstances might have changed in the time period being comparing against which makes it a dangerous method to use. That approach might falsely deem a change to be a “winner” or a “loser”. The only scientific way to get accurate results is to conduct an experiment where new versions of whatever is being changed are measured against the original (or control) version and the results are them compared, debated and measured.


Conversion Rate = Unique Conversions / Users
Conversion Rate = Conversions / Sessions

CRO means improving this number (ideally by increasing the numerator and not decreasing the denominator). Sometimes this means asking “what’s wrong with the site?” and other times asking “how can it be better?”. Whatever you do, you need to be able to measure it like a scientist and not like a marketer.

In my next post I discuss some common misconceptions about conversion rate optimisation.


I don’t have anyone to link to right now so I will link to our videos page and the London meetup page.

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